[en] We investigated the nature and the range of interactions between negatively charged polyelectrolyte-coated surfaces as a function of salt concentration using the surface forces apparatus. The measured force profiles (interaction forces versus separation distance) are purely repulsive and show long-range electrostatic and short-range steric interactions. The measured range of interaction in salt-free as well as in low ionic strengths extends well beyond the contour length of the polyelectrolyte chain. It is shown that the interaction range between the ionic brush layers and the grafting density depend on the ionic strength of the solution. In salt-free solution, the counterions associated with polyelectrolyte cause the chains to stretch and give rise to long-range double-layer electrostatic repulsions between the opposing chains. When salt is added to the system, the electrostatic interactions are partially screened and the polymer chain regains its flexibility and therefore the range of interactions is reduced. The measured total range of interaction exhibits relatively weaker dependence on the salt concentration. We find that our force−distance profiles with added salt in a compressed regime can be very well described by the Pincus scaling model.
Research Center/Unit :
Center for Education and Research on Macromolecules (CERM)
Disciplines :
Materials science & engineering Chemistry
Author, co-author :
Abraham, T.; Laval University, Sainte Foy, Canada > Department of Chemical Engineering and CERSIM
Giasson, S.; Laval University, Sainte Foy, Canada > Department of Chemical Engineering and CERSIM
Gohy, Jean-François; Université de Liège - ULiège > Department of Chemistry > Center for Education and Research on Macromolecules (CERM)
Jérôme, Robert ; Université de Liège - ULiège > Department of Chemistry > Center for Education and Research on Macromolecules (CERM)
Language :
English
Title :
Direct measurements of interactions between hydrophobically anchored strongly charged polyelectrolyte brushes
Publication date :
02 May 2000
Journal title :
Langmuir
ISSN :
0743-7463
eISSN :
1520-5827
Publisher :
Amer Chemical Soc, Washington, United States - Washington
NSERC - Natural Sciences and Engineering Research Council FCAR - Fonds pour la Formation de chercheurs et l'Aide à la recherche BELSPO - Politique scientifique fédérale
Abe, T.; Kurihara, K.; Higashi, N.; Niwa, M. J. Phys. Chem. 1995. 99, 1820.
Kelley, T. W.; Schorr, P. A.; Kristin, D.,.J.; Tirrell M.; Friabie, C. D. Macromolecules 1998, 31, 4297.
Israelachvili, J. N.; Adams, G. E. J. Chem. Soc., Faraday Trans. 1978, 174, 975.
Israelachvili, J. N. J. Colloids Interface Sci. 1973, 44, 259.
Israelachvili J. N. Intermolecular & Surface Forces, 2nd ed.; Academic Press: London, 1992; Chapter 10.
Gaines, G. L., Jr. Insoluble monolayers at gas liquid interfaces; Interscience: New York, 1966.
Roberts G. G. Langmuir-Blodgett films; Plenum Press: New York, 1991.
Cleasson, P. M.; Blom, C. E.; Heder, P. C.; Ninham, B. W. J. Colloid Interface Sci. 1986, 114, 234.
Wood, J.; Sharma, R. Langmuir 1995, 11, 4797.
Chan, D. Y.; Pasley, R. M.; White, L. R. J. Colloid Interface Sci. 1980, 77, 283.
Grabbe, A. Langmuir 1993, 9, 797.
Israelachvili, J. N. Intermolecular & Surface Forces, 2nd ed.; Academic Press: London, 1992; Chapter 12.
Israelachvili, J. N. Intermolecular & Surface Forces, 2nd ed.; Academic Press: London, 1992; Chapter 14.
There is a significant difference between estimated Debye lengths obtained from force curves and expected Debye lengths based on the salt concentrations used.
The use of constant numerical prefactor can be justified as the scaling arguments do not provide the numerical prefactor.
Recent ellipsometric measurements show that the equilibrium adsorption surface density (d-2) of the same diblock coplymer (PtBMA-b-PGMAS) on hydrophobized silica surfaces from 100 ppm PtBMA-b-PGMAS solution increases as a function of salt concentration with a power law dependence d-2 ∝ C81/4. Therefore, the d value for curve fitting is adjusted such that the grafting density increases with added salt concentrations. For details on surface density measurements see: Abraham, T.; Giasson, S.; Gohy, J. F.; Jérôme, R.; Müller, B.; Stamm, M. To appear in Macromolecules. See also: Meadows, J.; Williams, P. A.; Garvey, M.; Harrop, R.; Phillips, G. O. J. Colloid Interface Sci. 1989, 132, 319.
Recent ellipsometric measurements show that the equilibrium adsorption surface density (d-2) of the same diblock coplymer (PtBMA-b-PGMAS) on hydrophobized silica surfaces from 100 ppm PtBMA-b-PGMAS solution increases as a function of salt concentration with a power law dependence d-2 ∝ C81/4. Therefore, the d value for curve fitting is adjusted such that the grafting density increases with added salt concentrations. For details on surface density measurements see: Abraham, T.; Giasson, S.; Gohy, J. F.; Jérôme, R.; Müller, B.; Stamm, M. To appear in Macromolecules. See also: Meadows, J.; Williams, P. A.; Garvey, M.; Harrop, R.; Phillips, G. O. J. Colloid Interface Sci. 1989, 132, 319.
In Pincus scaling model the interchain distance d is assumed to be fixed. For fixed rf, the LB should vary with any dependable parameters such as NB or Cs with scaling exponents 1 and -1/3, respectively. However, for a variable surface density of adsorbed chain (that is the case here, see ref 40), it is not the layer thickness LB that should vary with any dependable parameters but rather the product LBd2/3 as noted in ref 7.
For salted brush in the regime where added salt concentration far exceeds the countenon concentration, Zhulina et al. 21 predict LBd2/3 ≈ Cs-1/3, consistent with the Pincus predictions.
Odijk, L.; Hauwaart. D. J. Polym. Sci., Polym. Phys. 1978, 16 627.
In ref 22, the authors follow the line of the Pincus model in ignoring chain stiffness but modify the excluded volume in the form of ve ≈ lp2(1/ks) (originally derived by Odijk and Hauwaart 43) and incorporate into the Daoud-Cotton model. Accordingly their model predicts LBd2/3 ≈ Cs-1/6.
